Screen for half-tone process



(NoModel.)

M. LEVY. SCREEN EOE HALE TONE PEoGEss.

No. 521,659. Patented June 19, 1894.

w wml [7er/erbr- Nrrau STATES MAX LEXIY, OF PHILADELPHIA, PENNSYLVANIA.

SCREEN Fos HALF-Tools Psc-cass.

SPECIFICATION forming part of Letters Patent No. 521,659, dated June 19, 189s.

Application filed March 1, 1894:.

ing to be a full, clear, and exact description of the invention, such 'as will enable others skilled in the art to whch'it appertains to' make and use the same, reference being had to the accompanying drawings, and to letters of reference marked thereon, which form a part of this specification.

Thisiuvention relates to photomechanical engraving in halt-tone.

A The object of the invention is to provide .photomechanical half-tone printing surfaces having a different texture from that produced by the means in current use, and at the same time render a more accurate 'definition of the details of the subject and a. greater Variety of gradations @flight and shade than is obtained by theusual methods,

I n all 'the methods which are at present in use of producing halt-tone printing surfaces by means of a lined or-4 cross-lined screen the grain or texture consists oi'a'seres of lsubdivisions of the surface which, while the individual elements of the series differ from each other, are still geometrically alike; that is, for any particular shade there would be dots, lines or cross-lines which have the same geometrical relation to each other, whatever their individual character, and the same is true for This invention consistsin an improvement by means of which each vsubdivision of the printing surface and the resulting texture of the printed impression consist of regularly disposed groups of dots, lines and stipples,

.and the individual members of each group tiene to the light differing in value from each other and also arranged in groups. These seau No. 501,934. or@ man.)

groups may each consist of two, three, four or more individual members, and the chief condition is that both transparent and opaque members should differ in size from one another. Such a screen may be formed of lines alternately thick and thin and crossed at or nearly at right angles, and in this case one of the sets of lines in each direction must be displaced from the middle of the space formed bythe complementary set' of lines, so as to form four transparent apertures varying inv size, and the intersections of the thinner and 'thicker lines will? form the necessary opaque obstructions, which also vary in size.

Figure 1 shows a grating or screen of this construction, and A and a representa series of two sets ofparallel opaque lines alternating thinner and thicker, and A' a a similar series of two sets of parallel opaque lines, but are somewhat farther apart than the set A a. This arrangement will give a dierent sized obstruction to the light, first, the intersections ot the lines A and A", second the intersections of the lines A and a and A and `aand third the intersections of the lines a and a. The interval B will be smaller than AB and the interval b the same size as b,

which will result in four different sized transparent apertures.

The screen may also be formed by having a series of parallel lines alternately thinner and thicker crossed by a single series of parallel lines, as shown, in Fig, 2. This arrangemeut aords two different sized transparent apertures B and b and two different opaque 4obstructions formed by the intersections of the lines A and A and of the lines A and a.

Fig. 3 shows a screen constructed in accordance with my invention, and which 'consists of four sets of parallel lines crossing in different directions, two sets crossed at right angles to each other and the vother two sets also crossed at right angles to each other and g at an angle of forty-,tive degrees to the iirst two sets, the spacing-coinciding exactlyto the relation between the sides and hypotenuse of a right angled triangle, but the inter- I sections are so disposed that the resulting apertures shall vary in size, and in this casethere will be two dierent sized obstructions ico to the lighnormed first by the intersections of the two lines and a, and second-oi these 4picture or IlA senese same two and A n." added thereto. Fig. 4 `is a view showing the texture of the resulting printing surface.

Any of these forms of screensA may be formed by photographic reproduction from a suitably `ruled original, or produced in the manner set forth in the patent granted to L. E9. Legvgy and Max Levy, February 21,1893. N o. 4 2,3 r

The screens here described are used in the same manner "as the ordinary cross-lined screen, by being placed in the camera in front of the sensitive plate, and it is obvious that from such a screen the resulting picture will have in the highest lights dots representing only the largest opaque obstruction in `each groupwhile in a shade darker there will be added a smaller dot representing the next sized intersection, and so on if there are more sizes. The same is true in the shadows-as these4 become darker thelight admitted by the smaller apertures willr be ineffectual to form alprinting dot, and these willdisappear in series 'as the shadows deepen until the deepest shadows before the solid black surface will have only dots representing the largest sized apertures. This will, as before pointedout, greatly facilitate the rendering ci tine detail, and by reason oi' the resulting variety of textures produce a far greater variety of tones than can be obtained by the means at present in use and which givc the possibility of only one gradation of dots` in the lights and only one gradation of dots in the shadows.

In tli'ese screens all the spaces formed by the various lines are left quite unobstructed and as transparent as it is possible to obtain them.

The resulting picture produced by means of the screens described will have the following characteristics: In the highest light, not pure white, there will be a series of line black dots which will correspond with the boldest intersections in the screen; as the shade becomes darker these dots will become slightly larger, and in the lighter middle tints there will be present a second series of smaller black dots corresponding with the lesser intersections of These two series of dots will increase in size as the shade deepens until they form continuous lines spaced similar to the corresponding lines in the screen.

'disappear until in the black lines in the screen.

As'the shade bel comes still deeper the dots represented by the l smallest apertures in the screen will disappear, and as the shades become deeper and deeperfrom this point on the dots successively represented by the decreasing sized transparent apertures in the screen will successivel 6o the deepest shadow whic 1s not black, there will be u t one white dot in each group, and this dot will represent. the

largest transparent of the screen. i

Having thus described my invention, what I claim as new, and desire to secure by. Letters Patent, is'- 1. A grating or screen tor the purpose set forth, which consists of parallel lines of varying thickness and distance apart and crossed so as to formtransparent apertures of varying sizes arranged 'in groups.

In a grating or screen for the purpose set forth, the combination, of alternately thinn'er and thicker lines spaced at alternately greater and lessdistance apart and crossed by a similar series of lines similarly placed.

3. Avgrating or screen for the purpose set forth, the combination, of alternately thinner and thicker parallel lines spaced at alternately greater and less Vdistance apart and xrossed by a singleset of uniform parallel mes.

4. In a-grating or screen for' the purpose set forth,`the combination 'with two sets of lines crossed at right angles with each other, of two other sets' of lines crossing the first two sets diagonally at regular intervals forming different sized transparentapertures arranged in groups.

5. In a grating aperture in' each group set forth, the combination with two sets of lines crossed at rig t angles with each other, of two other sets of lines crossing the firstl two sets diagonally at regular intervals, forming at their intersections different sized obstructions arranged in groups. 6. .A photomechanical lhnll-tone printingsurface the subdivisions of `which consist of regularly disposed groups Ot dots the indi vidual members-ot each group differing trout. cach other.

In testimony whereof I aiix ray signature in* presence ot' two witnesses.

MAX LEVY. Witnesses:

HENRY LEWIS WALKER', F. ERMANN.

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